Discuz! X5.0 releases 20260320 through 20260501 contains an authentication bypass vulnerability that allows unauthenticated remote attackers to gain unauthorized access to database backup and restore functionality by exploiting a shared cryptographic key between UCenter integration and the database backup API exposed by dbbak.php. Attackers can inject a crafted payload through the username parameter during login to abuse the encryption oracle in logging_ctl::logging_more(), obtain a legitimately signed token, and use it to bypass authorization for database export and import operations, with the additional ability to trigger a race condition to impersonate arbitrary users.
Discuz! X5.0 shares a cryptographic key between UCenter integration and the database backup API exposed by the dbbak.php file. An attacker injects a crafted payload via the username parameter during login, exploiting the so-called encryption oracle in the logging_ctl::logging_more() method, which allows obtaining a legitimately signed token. This token is then used to bypass authorization during database export and import operations. Additionally, the vulnerability enables triggering a race condition to impersonate any user in the system.
An attacker can gain unauthorized access to complete database backups (potentially containing user data, passwords, and sensitive information) and restore or overwrite the database, as well as impersonate any user in the system.
Apply the patch available in the producer's repository (commit 9962dad52c4c6999dabaf91ecd70377c680ff3c6 in the Gitee repository). Immediate update to the version released after 20260501 is recommended. Until the patch is implemented, consider restricting network access to the dbbak.php file at the firewall or web server level.
Discuz! X5.0 in versions released from 20260320 to 20260501 (releases 20260320 through 20260501)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X